This invention relates generally to capacitors, and more particularly to capacitors made with high dielectric constant dielectric materials having reduced leakage current, and to methods of making such capacitors and their incorporation into DRAM cells.
The increase in memory cell density in DRAMs presents semiconductor chip designers and manufacturers with the challenge of maintaining sufficient storage capacity while decreasing cell area. One way of increasing cell capacitance is through cell structure techniques, including three dimensional cell capacitors. The continuing drive to decrease size has also led to consideration of materials with higher dielectric constants for use in capacitors. Dielectric constant is a value characteristic of a material and is proportional to the amount of charge that can be stored in a material when the material is interposed between two electrodes. Promising dielectric materials include BaxSr(1xe2x88x92X)TiO3 (xe2x80x9cBSTxe2x80x9d), BaTiO3, SrTiO3, PbTiO3, Pb(Zr,Ti)O3 (xe2x80x9cPZTxe2x80x9d), (Pb,La)(Zr,Ti)O3 (xe2x80x9cPLZTxe2x80x9d), (Pb,La)TiO3 (xe2x80x9cPLTxe2x80x9d), KNO3, Nb2O5, Ta2O5, and LiNbO3, all of which have high dielectric constants making them particularly desirable for use in capacitors. However, the use of these materials has been hampered by their incompatability with current processing techniques and their leakage current characteristics. For example, present RuOx/Ta2O5/TiN capacitor structures show several orders of magnitude leakage degradation after subsequent rapid thermal processing (RTP) at 650xc2x0 C. in a nitrogen atmosphere.
Producing a metal/insulator/metal structure that does not degrade under subsequent high temperature processing remains an unsolved problem for incorporating high dielectric constant (high K) materials into advanced DRAM cells. A concern with using metal electrodes in the capacitor structure is that there is vacancy diffusion during subsequent high temperature treatments. At the electrode interface boundary, it would be advantageous to have an electrode that could supply oxygen to fill oxygen vacancies.
The use of oxygen-doped, sputter deposited platinum (PVD Pt) electrodes have been proposed in the literature. Y. Tsunemine, et al., xe2x80x9cA manufacturable integration technology of sputter-BST capacitor with a newly proposed thick Pt electrode,xe2x80x9d 1998 IEDM 30.3.1. However, PVD Pt electrodes cannot be used in capacitor container structures. As shown in FIG. 1, when a layer of Pt 12 is sputter deposited in a container structure 10, the deposition produces uneven layer thicknesses. Because conformal coverage is required for capacitor container structures, sputter deposition cannot be used.
Therefore, there remains a need in this art for improved processes for incorporating high dielectric constant dielectric materials into capacitor constructions and for capacitors containing these materials.
The present invention meets these needs by providing a stabilized capacitor having improved leakage current characteristics using high dielectric constant oxide dielectric materials, and methods of making such capacitors. By xe2x80x9chigh dielectric constant oxide dielectricxe2x80x9d materials we mean oxides of barium, titanium, strontium, lead, zirconium, lanthanum, and niobium, including, but not limited to BaxSr(1xe2x88x92x)TiO3 (xe2x80x9cBSTxe2x80x9d), BaTiO3, SrTiO3, Ta2O5, Nb2O5, PbTiO3, Pb(Zr,Ti)O3 (xe2x80x9cPZTxe2x80x9d), (Pb,La)(Zr,Ti)O3 (xe2x80x9cPLZTxe2x80x9d), (Pb,La)TiO3 (xe2x80x9cPLTxe2x80x9d), KNO3, and LiNbO3 and having a dielectric constant of at least about 20.
In accordance with one aspect of the present invention, the method includes depositing a lower electrode on a semiconductor substrate, oxygen doping the lower electrode, oxidizing an upper surface of the oxygen-doped lower electrode, depositing a high dielectric constant oxide dielectric material on the oxidized oxygen-doped metal electrode, and depositing an upper layer electrode on the high dielectric constant oxide dielectric material. The lower electrode is preferably selected from the group consisting of TiN, Pt, Rh, Ru, Re, Ir, Os, and alloys and intermetallic compounds thereof. The upper layer electrode is preferably selected from the group consisting of TiN, W, Pt, Rh, Ru, Re, Ir, Os, and alloys and intermetallic compounds thereof. The high dielectric constant oxide dielectric material is preferably selected from the group consisting of Ta2O5 and BaxSr(1xe2x88x92x)TiO3.
The oxygen doping is preferably obtained by chemical vapor depositing the lower electrode in an oxygen-containing environment. By xe2x80x9coxygen containing environment,xe2x80x9d it is meant an atmosphere which contains gaseous oxygen. The upper layer electrode is also preferably chemical vapor deposited in an oxygen-containing environment. In a preferred form, the method deposits the lower electrode layer and/or the upper layer electrode using chemical vapor deposition (CVD) techniques.
Another aspect of the invention provides a capacitor including an oxygen-doped lower electrode having an oxidized surface, a high dielectric constant oxide dielectric material adjacent to the oxidized surface of the oxygen-doped lower electrode, and an upper layer electrode adjacent to the high dielectric constant oxide dielectric material. The lower electrode is preferably selected from the group consisting of TiN, Pt, Rh, Ru, Re, Ir, Os, and alloys and internetallic compounds thereof. The upper layer electrode is preferably selected from the group consisting of TiN, W, Pt, Rh, Ru, Re, Ir, Os, and alloys and intermetallic compounds thereof. The high dielectric constant oxide dielectric material is preferably selected from the group consisting of Ta2O5 and BaxSr(1xe2x88x92x)TiO3.
Both the lower electrode and the upper layer electrode are preferably deposited using chemical vapor deposition (CVD) techniques. Also, preferably, both the lower electrode and the upper layer electrode are doped with oxygen.
The capacitor may also include a first layer of a chemical vapor deposited lower electrode beneath the oxygen-doped layer of the lower electrode, and a second layer of a chemical vapor deposited upper layer electrode adjacent to the first layer of the upper layer electrode.
Accordingly, it is a feature of the present invention to provide a stabilized capacitor having improved leakage current characteristics using high dielectric constant oxide dielectric materials, their incorporation into DRAM cells, and methods of making such capacitors. These, and other features and advantages of the present invention, will become apparent from the following detailed description, the accompanying drawings, and the appended claims.